1. Technical Field
The present invention relates to a pulsed light source for the removal of biological tissue with light means and a controller for controlling the light means in such a way that the light means generate on the one hand ablation pulses with a particular pulse frequency and an irradiance sufficient for ablation of tissue and on the other hand a coagulation radiation with an irradiance which is certainly sufficient for a heating of tissue, but not for an ablation of tissue. In particular the present invention relates to a pulsed light source of the kind described above for use in the dental field.
2. Background Information
As is known, biological tissue can be removed with the aid of high-energy light radiation, for example with laser radiation. The surrounding tissue is heated, however, if a sufficiently intensive light is used, the degree of said heating being dependent in particular both on the wavelength of the radiation used and the absorption coefficient of the tissue, said absorption coefficient being dependent on said wavelength, and on the irradiance. On the removal or cutting of biological tissue the depression thereby caused or the cut is surrounded by a carbonisation zone, a zone loosened by vacuoles, a coagulation zone and a reversibly thermally damaged area. In order to achieve as good a wound-healing process as possible and as little damage to the tissue as possible, the smallest thermal effects as possible are advantageous. The formation of a carbonisation layer, i.e. the carbonisation of the tissue surface, such as occurs with cutting with continuous wave lasers, is undesirable. The coagulation zone produced by the heating and the associated hemostasis is advantageous, however, if the capillary layer is damaged during the treatment of the tissue, since otherwise the escaping blood would affect the removal of the tissue. The coagulation zone produced by the heating therefore makes non-bleeding cuts possible.
It is known that tissue can be removed with pulsed light sources of high output and a wavelength in the ultraviolet or infrared range without carbonisation of the tissue surface and with relatively little thermal damage. A relatively small coagulation zone is moreover formed, which has for example a thickness of only 30-40 .mu.m. A small coagulation zone of this kind is advantageous in particular for the treatment of superficial skin lesions and for cosmetic surgery, since damage to the tissue which goes beyond the removal of the tissue is avoided. As has already been described before, however, it is not possible with such a small coagulation zone, if the capillary layer is affected, for a non-bleeding cut to be obtained, since the escaping blood then affects the removal of the tissue and in certain cases even impedes it.
There was therefore a requirement for a light source for the removal of biological tissue, by means of which on the one hand tissue can be removed as precisely as possible and with as few thermal side-effects as possible and without carbonisation of the tissue surface and on the other a coagulation zone specific to the respective application can be produced and formed. To this end a pulsed light source was proposed in DE-C1-195 21 003 according to the preamble of claim 1. Said pulsed light source comprises a controller which controls the light source in such a way that the light source generates with a predetermined pulse frequency short ablation pulses for the ablation, i.e. for the removal, of the tissue, wherein each ablation pulse is followed by a coagulation irradiation whose irradiance does not suffice for the removal of tissue, but leads to a heating of the tissue, which in turn supports the formation of a coagulation zone. The generation of the ablation pulses therefore makes it possible to achieve on the one hand, without formation of a carbonisation layer, a very effective thermo-mechanical ablation process with relatively little thermal damage to the remaining tissue. This is of particular interest in particular for the treatment of superficial skin lesions or for cosmetic surgery. On the other hand there is promoted with the artificial heating of the tissue which results from the coagulation irradiation following each ablation pulse the formation of a coagulation zone, wherein the associated hemostasis makes non-bleeding cuts possible even if the capillary layer of the tissue is damaged, i.e. even if the capillary layer of the tissue is damaged the ablation is not affected by escaping blood.
According to DE-C1-195 21 003 each ablation pulse is always followed by a coagulation radiation, wherein the coagulation radiation can likewise be realised in the form of pulses. The generation of the coagulation radiation is however dependent in each case on the generation of a preceding ablation pulse. This makes the control of the pulsed light source by the controller labourious.